ASTM E839-23

Standard Test Methods for Sheathed Thermocouples and Sheathed Thermocouple Cable

SIGNIFICANCE AND USE
5.1 This standard provides a description of test methods used in other ASTM specifications to establish certain acceptable methods for characterizing thermocouple assemblies and thermocouple cable. These test methods define how those characteristics shall be determined.  
5.2 The usefulness and purpose of the included tests are given for the category of tests.  
5.3 Warning—Users should be aware that certain characteristics of thermocouples might change with time and use. If a thermocouple’s designed shipping, storage, installation, or operating temperature has been exceeded, that thermocouple’s moisture seal may have been compromised and may no longer adequately prevent the deleterious intrusion of water vapor. Consequently, the thermocouple’s condition established by test at the time of manufacture may not apply later. In addition, inhomogeneities can develop in thermoelements because of exposure to higher temperatures, even in cases where maximum exposure temperatures have been lower than the suggested upper use temperature limits specified in Table 1 of Specification E608/E608M. For this reason, calibration of thermocouples destined for delivery to a customer is not recommended. Because the emf indication of any thermocouple depends upon the condition of the thermoelements along their entire length, as well as the temperature profile pattern in the region of any inhomogeneity, the emf output of a used thermocouple will be unique to its installation. Because temperature profiles in calibration equipment are unlikely to duplicate those of the installation, removal of a used thermocouple to a separate apparatus for calibration is not recommended. Instead, in situ calibration by comparison to a similar thermocouple known to be good is often recommended.
SCOPE
1.1 This document lists methods for testing Mineral-Insulated, Metal-Sheathed (MIMS) thermocouple assemblies and thermocouple cable, but does not require that any of these tests be performed nor does it state criteria for acceptance. The acceptance criteria are given in other ASTM standard specifications that impose this testing for those thermocouples and cable. Examples from ASTM thermocouple specifications for acceptance criteria are given for many of the tests. These tabulated values are not necessarily those that would be required to meet these tests, but are included as examples only.  
1.2 These tests are intended to support quality control and to evaluate the suitability of sheathed thermocouple cable or assemblies for specific applications. Some alternative test methods to obtain the same information are given, since in a given situation, an alternative test method may be more practical. Service conditions are widely variable, so it is unlikely that all the tests described will be appropriate for a given thermocouple application. A brief statement is made following each test description to indicate when it might be used.  
1.3 The tests described herein include test methods to measure the following properties of sheathed thermocouple material and assemblies.  
1.3.1 Insulation Properties:  
1.3.1.1 Compaction—direct method, absorption method, and tension method.
1.3.1.2 Thickness.
1.3.1.3 Resistance—at room temperature and at elevated temperature.  
1.3.2 Sheath Properties:  
1.3.2.1 Integrity—two water test methods and mass spectrometer.
1.3.2.2 Dimensions—length, diameter, and roundness.
1.3.2.3 Wall thickness.
1.3.2.4 Surface—gross visual, finish, defect detection by dye penetrant, and cold-lap detection by tension test.
1.3.2.5 Metallurgical structure.
1.3.2.6 Ductility—bend test and tension test.  
1.3.3 Thermoelement Properties:  
1.3.3.1 Calibration.
1.3.3.2 Homogeneity.
1.3.3.3 Drift.
1.3.3.4 Thermoelement diameter, roundness, and surface appearance.
1.3.3.5 Thermoelement spacing.
1.3.3.6 Thermoelement ductility.
1.3.3.7 Metallurgical structure.  
1.3.4 Thermocouple Assembly Properti...

General Information

• Status: Published
• Publication Date: 31-Oct-2023
• ICS: 17.200.20 - Temperature-measuring instruments
• Technical Committee: E20 - Temperature Measurement
• Drafting Committee: E20.14 - Thermocouples - Testing

Relations

• Replaces: ASTM E839-11(2016)e1 - Standard Test Methods for Sheathed Thermocouples and Sheathed Thermocouple Cable
• Effective Date: 01-Nov-2023
• Refers: ASTM E344-23 - Terminology Relating to Thermometry and Hydrometry
• Effective Date: 01-Dec-2023
• Referred By: ASTM E2821-20 - Standard Specification for Compacted Mineral-Insulated, Metal-Sheathed Cable Used in Industrial Resistance Thermometers
• Effective Date: 01-Nov-2023
• Referred By: ASTM E2488-22 - Standard Guide for the Preparation and Evaluation of Liquid Baths Used for Temperature Calibration by Comparison
• Effective Date: 01-Nov-2023
• Referred By: ASTM E2846-20 - Standard Guide for Thermocouple Verification
• Effective Date: 01-Nov-2023
• Referred By: ASTM E1350-18(2023) - Standard Guide for Testing Sheathed Thermocouples, Thermocouple Assemblies, and Connecting Wires Prior to, and After Installation or Service
• Effective Date: 01-Nov-2023
• Referred By: ASTM E608/E608M-13(2019) - Standard Specification for Mineral-Insulated, Metal-Sheathed Base Metal Thermocouples
• Effective Date: 01-Nov-2023
• Referred By: ASTM E344-20 - Terminology Relating to Thermometry and Hydrometry
• Effective Date: 01-Nov-2023
• Referred By: ASTM E2877-12(2019) - Standard Guide for Digital Contact Thermometers
• Effective Date: 01-Nov-2023
• Referred By: ASTM E235/E235M-23 - Standard Specification for Type K and Type N Mineral-Insulated, Metal-Sheathed Thermocouples for Nuclear or for Other High-Reliability Applications
• Effective Date: 01-Nov-2023
• Referred By: ASTM G151-19 - Standard Practice for Exposing Nonmetallic Materials in Accelerated Test Devices that Use Laboratory Light Sources
• Effective Date: 01-Nov-2023
• Referred By: ASTM E585/E585M-23 - Standard Specification for Compacted Mineral-Insulated, Metal-Sheathed, Base Metal Thermocouple Cable
• Effective Date: 01-Nov-2023

Overview

ASTM E839-23: Standard Test Methods for Sheathed Thermocouples and Sheathed Thermocouple Cable provides detailed test methods for evaluating Mineral-Insulated, Metal-Sheathed (MIMS) thermocouple assemblies and cables. Administered by ASTM Committee E20 on Temperature Measurement, this standard supports users, manufacturers, and quality professionals in assessing critical characteristics related to insulation, sheath integrity, thermoelement performance, and assembly properties. While ASTM E839-23 describes recommended test methods, the acceptance criteria for thermocouples and cables are specified in other relevant ASTM standards.

Key Topics

Insulation Properties

• Compaction: Methods including direct, absorption, and tension tests to evaluate insulation density and ensure thermoelements are locked in place, improving mechanical stability and heat transfer.
• Thickness: Verification of insulation thickness using metallographic examination or radiography, ensuring design specifications are met for performance and safety.
• Resistance: Measurement of insulation resistance at room and elevated temperatures to detect moisture or impurities that may affect thermocouple accuracy and service life.

Sheath Properties

• Integrity: Water tests and mass spectrometer analysis are employed to detect leaks that could allow moisture or gas intrusion, which compromise insulation and measurement reliability.
• Dimensions: Assessment of sheath length, diameter, and roundness for precise fit and compatibility with instrumentation requirements.
• Wall Thickness & Surface: Determination of sheath wall thickness and surface quality using visual, dye penetrant, and cold-lap detection methods.
• Metallurgical Structure & Ductility: Analysis to ensure sufficient durability and mechanical performance during installation and operation.

Thermoelement Properties

• Calibration and Homogeneity: Ensures temperature-electromotive force (emf) relationship is within standardized tolerances before initial use; notes that recalibration after service may not reflect installation-specific conditions.
• Drift and Ductility: Evaluates changes in thermoelement stability over time and mechanical flexibility.
• Diameter and Surface Evaluation: Measurement and inspection processes to verify conformance to design requirements.

Assembly Properties

• Electrical Properties: Tests for circuit continuity, loop resistance, and connector polarity to guarantee reliable operation.
• Radiographic Inspection: Non-destructive examination to identify internal faults in welds and assemblies.
• Thermal Response and Cycling: Evaluates thermal response times and resistance to temperature cycling, assuring suitability for dynamic process environments.

Applications

ASTM E839-23 is widely applied in quality control, specification compliance, and suitability assessment for sheathed thermocouples and thermocouple cable in critical industries such as:

• Industrial process control and automation
• Power generation and energy
• Aerospace and defense
• Chemical and petrochemical processing
• Laboratory and test measurement settings

The included test methods help manufacturers and users ensure that thermocouple products conform to applicable specifications and are suitable for intended service conditions, especially in high temperature and reliability-focused applications.

Related Standards

Organizations rely on ASTM E839-23 in conjunction with related ASTM and industry standards for comprehensive testing, specification, and terminology:

• ASTM E608/E608M - Mineral-Insulated, Metal-Sheathed Base Metal Thermocouples
• ASTM E585/E585M - Compacted Mineral-Insulated, Metal-Sheathed, Base Metal Thermocouple Cable
• ASTM E1129/E1129M, E1684 - Thermocouple connectors and miniature connectors
• ASTM E780 - Insulation resistance measurement at room temperature
• ASTM E220, E207 - Calibration and EMF test methods
• ASTM E165 - Liquid penetrant testing for defect detection
• ANSI B46.1 - Surface texture standards

Using ASTM E839-23 alongside these documents ensures a robust framework for thermocouple cable and assembly quality and reliability, supporting effective temperature measurement across demanding environments.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E839 − 23 An American National Standard
Standard Test Methods for
Sheathed Thermocouples and Sheathed Thermocouple
Cable
This standard is issued under the fixed designation E839; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 1.3.2.4 Surface—gross visual, finish, defect detection by
dye penetrant, and cold-lap detection by tension test.
1.1 This document lists methods for testing Mineral-
1.3.2.5 Metallurgical structure.
Insulated, Metal-Sheathed (MIMS) thermocouple assemblies
1.3.2.6 Ductility—bend test and tension test.
and thermocouple cable, but does not require that any of these
tests be performed nor does it state criteria for acceptance. The 1.3.3 Thermoelement Properties:
acceptance criteria are given in other ASTM standard specifi-
1.3.3.1 Calibration.
cations that impose this testing for those thermocouples and
1.3.3.2 Homogeneity.
cable. Examples from ASTM thermocouple specifications for
1.3.3.3 Drift.
acceptance criteria are given for many of the tests. These
1.3.3.4 Thermoelement diameter, roundness, and surface
tabulated values are not necessarily those that would be
appearance.
required to meet these tests, but are included as examples only.
1.3.3.5 Thermoelement spacing.
1.2 These tests are intended to support quality control and to
1.3.3.6 Thermoelement ductility.
evaluate the suitability of sheathed thermocouple cable or
1.3.3.7 Metallurgical structure.
assemblies for specific applications. Some alternative test
1.3.4 Thermocouple Assembly Properties:
methods to obtain the same information are given, since in a
1.3.4.1 Dimensions—length, diameter, and roundness.
given situation, an alternative test method may be more
1.3.4.2 Surface—gross visual, finish, reference junction end
practical. Service conditions are widely variable, so it is
moisture seal, and defect detection by dye penetrant.
unlikely that all the tests described will be appropriate for a
1.3.4.3 Electrical—continuity, loop resistance, and connec-
given thermocouple application. A brief statement is made
tor polarity.
following each test description to indicate when it might be
used. 1.3.4.4 Radiographic inspection.
1.3.4.5 Thermoelement diameter.
1.3 The tests described herein include test methods to
1.3.4.6 Thermal response time.
measure the following properties of sheathed thermocouple
material and assemblies. 1.3.4.7 Thermal cycle.
1.3.1 Insulation Properties:
1.4 The values stated in either SI units or inch-pound units
1.3.1.1 Compaction—direct method, absorption method,
are to be regarded separately as standard. The values stated in
and tension method.
each system may not be exact equivalents; therefore, each
1.3.1.2 Thickness.
system shall be used independently of the other. Combining
1.3.1.3 Resistance—at room temperature and at elevated
values from the two systems may result in non-conformance
temperature.
with the standard.
1.3.2 Sheath Properties:
1.5 This standard does not purport to address all of the
1.3.2.1 Integrity—two water test methods and mass spec-
safety concerns, if any, associated with its use. It is the
trometer.
responsibility of the user of this standard to establish appro-
1.3.2.2 Dimensions—length, diameter, and roundness.
priate safety, health, and environmental practices and deter-
1.3.2.3 Wall thickness.
mine the applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accor-
dance with internationally recognized principles on standard-
These test methods are under the jurisdiction of ASTM Committee E20 on
Temperature Measurement and is the direct responsibility of Subcommittee E20.14
ization established in the Decision on Principles for the
on Thermocouples - Testing.
Development of International Standards, Guides and Recom-
Current edition approved Nov. 1, 2023. Published November 2023. Originally
ɛ1
mendations issued by the World Trade Organization Technical
approved in 1989. Last previous edition approved in 2016 as E839 – 11 (2016) .
DOI: 10.1520/E0839-23. Barriers to Trade (TBT) Committee.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E839 − 23
2. Referenced Documents 2.3 Other Standard
USAEC Division of Reactor Development and Technology
2.1 ASTM Standards:
RDT Standard C 2-1T Determination of Insulation Com-
E3 Guide for Preparation of Metallographic Specimens
paction in Ceramic Insulated Conductors August 1970
E94 Guide for Radiographic Examination Using Industrial
Radiographic Film
3. Terminology
E112 Test Methods for Determining Average Grain Size
3.1 Definitions—The definitions given in Terminology E344
E165 Practice for Liquid Penetrant Testing for General
shall apply to these test methods.
Industry
3.2 Definitions of Terms Specific to This Standard:
E177 Practice for Use of the Terms Precision and Bias in
ASTM Test Methods 3.2.1 bulk cable, n—a single length of thermocouple cable
produced from the same raw material lots after completion of
E207 Test Method for Thermal EMF Test of Single Thermo-
fabrication.
element Materials by Comparison With Reference Ther-
moelement of Similar EMF-Temperature Properties
3.2.2 cable lot, n—a quantity of finished mineral–insulated,
E220 Test Method for Calibration of Thermocouples By
metal-sheathed thermocouple cable manufactured from tubing
Comparison Techniques
or other sheath material from the same heat, wire from the
E230 Specification for Temperature-Electromotive Force
same spool and heat, and insulation from the same batch, then
(emf) Tables for Standardized Thermocouples
assembled and processed together under controlled production
E235 Specification for Type K and Type N Mineral-
conditions to the required final outside diameter.
Insulated, Metal-Sheathed Thermocouples for Nuclear or
3.2.3 cold-lap, n—sheath surface defect where the sheath
for Other High-Reliability Applications
surface has been galled and torn by a drawing die and the torn
E344 Terminology Relating to Thermometry and Hydrom-
surface smoothed by a subsequent diameter reduction.
etry
3.2.4 insulation compaction density, n—the density of a
E585/E585M Specification for Compacted Mineral-
compacted powder is the combined density of the powder
Insulated, Metal-Sheathed, Base Metal Thermocouple
particles and the voids remaining after the powder compaction.
Cable
Sometimes the insulation compaction density is divided by the
E608/E608M Specification for Mineral-Insulated, Metal-
theoretical density of the powder particles to obtain a dimen-
Sheathed Base Metal Thermocouples
sionless fraction of theoretical density as a convenient method
E691 Practice for Conducting an Interlaboratory Study to
to express the relative compaction.
Determine the Precision of a Test Method
3.2.5 raw material, n—tubing or other sheath material,
E780 Test Method for Measuring the Insulation Resistance
insulation and wires used in the fabrication of sheathed
of Mineral-Insulated, Metal-Sheathed Thermocouples and
thermocouple cable.
Mineral-Insulated, Metal-Sheathed Cable at Room Tem-
3.2.6 short range ordering, n—the reversible short-ranged,
perature
order-disorder transformation in which the nickel and chro-
E1025 Practice for Design, Manufacture, and Material
mium atoms occupy specific (ordered) localized sites in the
Grouping Classification of Hole-Type Image Quality In-
Type EP or Type KP thermoelement alloy crystal structure.
dicators (IQI) Used for Radiography
E1129/E1129M Specification for Thermocouple Connectors
3.2.7 thermal response time, n—the time required for a
E1350 Guide for Testing Sheathed Thermocouples, Thermo-
sheathed thermocouple signal to attain the specified percent of
couple Assemblies, and Connecting Wires Prior to, and
the total voltage change produced by a step change of
After Installation or Service
temperature at the sheath’s outer surface.
E1684 Specification for Miniature Thermocouple Connec-
tors 4. Summary of Test Methods
E1751 Guide for Temperature Electromotive Force (emf)
4.1 Insulation Properties:
Tables for Non-Letter Designated Thermocouple Combi-
4.1.1 Compaction—These tests ensure that the insulation is
nations
compacted sufficiently (1) to prevent the insulation from
E2181/E2181M Specification for Compacted Mineral-
shifting during use with the possibility of the thermoelements
Insulated, Metal-Sheathed, Noble Metal Thermocouples
shorting to each other or to the sheath, and (2) to have good
and Thermocouple Cable
heat transfer between the sheath and the thermoelements.
4.1.2 Insulation Resistance—The insulation shall be free of
2.2 ANSI Standard
B 46.1 Surface Texture moisture and contaminants that would compromise the
voltage-temperature relationship or shorten the useful life of
the sheathed thermocouple. Measurement of insulation resis-
tance is a useful way to detect the presence of unacceptable
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
levels of impurities in the insulation.
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
4.2 Sheath Properties:
the ASTM website.
4.2.1 Integrity—These tests ensure that (1) the sheath will
Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036. be impervious to moisture and gases so the insulation and
E839 − 23
thermoelements will be protected, (2) surface flaws and cracks moisture seal may have been compromised and may no longer
that might develop into sheath leaks are detected, and (3) the adequately prevent the deleterious intrusion of water vapor.
sheath walls are as thick as specified. Consequently, the thermocouple’s condition established by test
4.2.2 Dimensions—Determination of length, diameter, and at the time of manufacture may not apply later. In addition,
sheath roundness are often necessary to assure proper dimen- inhomogeneities can develop in thermoelements because of
sional fit. exposure to higher temperatures, even in cases where maxi-
4.2.3 Sheath Ductility—The sheath shall be ductile enough mum exposure temperatures have been lower than the sug-
to bend the required amount without breaking or cracking. gested upper use temperature limits specified in Table 1 of
Specification E608/E608M. For this reason, calibration of
4.3 Thermoelement Properties Service Life:
thermocouples destined for delivery to a customer is not
4.3.1 Calibration—This test ensures that the temperature-
recommended. Because the emf indication of any thermo-
emf relationship initially corresponds to standardized toler-
couple depends upon the condition of the thermoelements
ances.
along their entire length, as well as the temperature profile
4.3.2 Size—The thermocouple sheath and thermoelement
pattern in the region of any inhomogeneity, the emf output of
sizes are related to the service life and the thermoelement
a used thermocouple will be unique to its installation. Because
spacing is related to possible low insulation resistance or
temperature profiles in calibration equipment are unlikely to
shorting.
duplicate those of the installation, removal of a used thermo-
4.3.3 Thermoelement Ductility—Ductility of the thermoele-
couple to a separate apparatus for calibration is not recom-
ments shall be sufficient to allow the assembly to be bent
mended. Instead, in situ calibration by comparison to a similar
during assembly or service without significant damage to the
thermocouple known to be good is often recommended.
thermoelements.
4.4 Thermocouple Assembly Properties—The criteria listed
6. General Requirements
above shall apply to both thermocouple assemblies and to bulk
6.1 All the inspection operations are to be performed under
cable. In addition, the following tests are important for
clean conditions that will not degrade the insulation, sheath, or
thermocouple assemblies.
thermoelements. This includes the use of suitable gloves when
4.4.1 Continuity—The loop continuity test assures that the
appropriate.
thermocouple assembly has a completed circuit.
4.4.2 Loop Resistance—The loop resistance test can detect 6.2 During all process steps in which insulation is exposed
shorted or damaged thermoelements. to ambient atmosphere, the air shall be clean, with less than
4.4.3 Polarity—The connector polarity test indicates 50 % relative humidity, and at a temperature between 20 °C
whether the connector is correctly installed. and 26 °C (68 °F and 79 °F).
4.4.4 Moisture Seal—The moisture seal at the reference
6.3 All samples which are tested shall be identified by
junction end of the thermocouple, if faulty, may allow con-
material code, and shall be traceable to a production run.
tamination of the insulation with moisture or gases.
4.4.5 Radiography—Radiographic examination of the junc-
7. Insulation Properties
tion and sheath closure weld can indicate faulty junctions and
7.1 Insulation Compaction Density—The thermal conduc-
sheath closures that will lead to early failure. Most internal
tivity of the insulation, as well as the ability of the insulation to
dimensions can also be measured from the radiograph.
lock the thermoelements into place, will be affected by the
4.4.6 Response Time—The thermal response time gives an
insulation compaction density.
indication of the quickness with which an installed thermo-
7.1.1 A direct method for measuring insulation compaction
couple will signal a changing temperature under the test
density is applicable if a representative sample can be sec-
conditions.
tioned so that the sample ends are perpendicular to the sample
4.4.7 Thermal Cycle—The thermal cycle test will offer
length and the sheath, thermoelements, and insulation form a
assurance that the thermocouple will not have early failure
smooth surface free of burrs. The procedure is as follows:
because of strains imposed from temperature transients.
7.1.1.1 Weigh the sample section,
7.1.1.2 Measure the sheath diameter and length with a
5. Significance and Use
micrometer,
5.1 This standard provides a description of test methods
7.1.1.3 Separate the insulation from the thermoelement and
used in other ASTM specifications to establish certain accept-
sheath with the use of an air abrasive tool,
able methods for characterizing thermocouple assemblies and
7.1.1.4 Weigh the thermoelements and sheath, and
thermocouple cable. These test methods define how those
7.1.1.5 Determine the sheath and thermoelements densities
characteristics shall be determined.
either by experiment or from references.
7.1.1.6 Determine the percentage of the maximum theoreti-
5.2 The usefulness and purpose of the included tests are
cal insulation density ρ as follows:
given for the category of tests.
%ρ 5 100~A 2 B!/$@0.785 C D 2 ~E/F1G/H!#J% (1)
5.3 Warning—Users should be aware that certain charac-
teristics of thermocouples might change with time and use. If
where:
a thermocouple’s designed shipping, storage, installation, or
A = total specimen mass, kg or lb,
operating temperature has been exceeded, that thermocouple’s
E839 − 23
compaction density where locking begins. This test can be
B = sheath and wires mass, kg or lb,
performed concurrently with the tension test in 8.5.3.
C = sheath diameter, m or in.,
7.2.1 Cut a test specimen about 0.5 m (20 in.) long from one
D = specimen length, m or in.,
E = sheath mass, kg or lb, end of a bulk cable length and strip both ends of the specimen
3 3
F = sheath density, kg/m or lb/in. ,
to expose a minimum of 10 mm (0.4 in.) of the thermoele-
G = wires mass, kg or lb,
ments.
H = wires density (averaged density if applicable), kg/m or
7.2.2 Without sealing the exposed insulation, clean the
lb/in. , and
thermoelements of insulation to provide good electrical contact
J = maximum theoretical density of the insulation, kg/m
and twist the wires together on one end to form a thermocouple
or lb/in. .
loop (see Fig. 1).
7.2.3 Measure the electrical resistance of the thermocouple
7.1.2 Alternately, a liquid absorption method for determin-
loop to 60.01 Ω and measure the length of the thermocouple
ing the insulation compaction density may be utilized for
loop to establish the electrical resistance per unit length.
MIMS samples with outside diameters 1.5 mm (.062 in.) and
7.2.4 Place the test sample in the tension testing machine so
larger. This method is based upon a procedure detailed in RDT
that (1) the grips clamp only on the sample sheath, (2) the force
C 2-1T and requires the following: (1) the sample ends shall be
will be applied longitudinally on the sheath, and (3) there is at
perpendicular to the sample axis and have a smooth, unglazed
least a 0.25 m (10-in.) distance between the grips where the
surface which will readily absorb liquid and shall be free of
force will be applied (see Fig. 2).
burrs, (2) the outer surfaces of the thermoelements and the
7.2.5 Attach an ohmmeter capable of measuring 60.01 Ω to
inner surface of the sheath shall be smooth and non-absorbent,
the exposed thermoelements and measure the resistance with
and (3) the insulation shall readily support capillary absorption
no tension force applied; also measure the distance between the
through the entire length of the sample. This procedure is as
tension tester grips to establish the initial length, L , of the test
follows:
sample that will be elongated.
7.1.2.1 Determine the density of kerosene for the tempera-
7.2.6 Calculate the initial resistance, R , of the test specimen
ture at which the measurement is being performed if other than
section that will be elongated, using the unit length electrical
16 ºC (60 ºF).
resistance obtained in 7.2.3.
7.1.2.2 Cut a specimen approximately 2.5 cm (1 in.) long.
7.2.7 Make a simultaneous record of the electrical resistance
7.1.2.3 Measure and record the inside diameter of the
and the elongation of the sheath while stretching the test
cable’s sheath and the outside diameter of the cable’s thermo-
sample until the thermoelements break.
elements to within .025 mm (.001 in.).
7.2.8 Examine the exposed ends of the thermoelements to
7.1.2.4 Weigh the specimen and record its weight. see whether they have been drawn into the insulation during
the elongation; any shortening of the exposed ends indicates
7.1.2.5 Measure and record the specimen’s length to within
low compaction of the insulation.
.025 mm (.001 in.) using a vernier caliper.
7.2.9 Plot the fractional change of resistance (∆R/R ) versus
7.1.2.6 Immerse the specimen in kerosene for a minimum of
the fractional change of length (∆L/L ). The slope of the plot
24 h.
reveals if the thermoelements were locked to the sheath
7.1.2.7 Re-weigh the specimen and record its weight.
throughout the plastic deformation of the sheath and, if not,
7.1.2.8 Determine the percentage of the maximum theoreti-
where the thermoelements began to elongate in a different
cal insulation density ρ as follows:
manner than the sheath. Examples of criteria to evaluate the
2 2
%ρ 5 100 1 2 Y 2 X /0.785 S L O 2 PR (2) insulation locking are given in X1.9
@ ~$ % $ %!#
7.3 Insulation Thickness Measurement—Determine the in-
L = specimen length, cm or in.,
sulation thickness, dimension C of Fig. 3, using either of the
O = inside diameter of sheath, cm or in.,
following methods:
P = number of thermoelements in the cable,
7.3.1 A metallographic mount, prepared in accordance with
R = outside diameter of thermoelements, cm or in.,
Practice E3, of a polished cross section of the thermocouple or
S = specific gravity of the kerosene absorbed at 16 °C
3 3
cable using a microscope having at least a 60× magnification
(60 °F), .81715 g/cm or .02952 lb/in ,
X = weight of the specimen before kerosene is absorbed, g
or lb, and
Y = weight of the specimen after kerosene is absorbed, g or
lb.
7.2 Insulation Compaction, Assurance Test—This is a de-
structive test on representative samples that determines if the
thermoelements are locked together with the sheath by the
compacted insulation, but this test does not measure the
compaction density per se. This test is the complement of the
tests of 7.1 and 7.2 that measures the insulation compaction
density but does not establish that the thermoelements are
FIG. 1 Specimen of Sheathed Thermocouple Cable Prepared for
locked to the sheath, since there is no established minimum Tension Testing
E839 − 23
destructive.) Sampling frequency shall be as stated in the
standard specification relevant to the subject thermocouple.
7.5.1 Thermocouple Assembly—Measure the electrical re-
sistance between the thermocouple circuit and the sheath of a
finished thermocouple assembly with a Style U ungrounded
measuring junction (see Fig. 3) using the technique of Test
Method E780. Insert the measuring junction of the finished
thermocouple into a furnace or constant temperature bath to a
depth that will yield maximum temperature stability (example:
20 sheath diameters). Then, the thermocouple junction can be
FIG. 2 The Thermocouple Positioned in the Tension Tester
heated to the test temperature. This procedure is not applicable
to a Style G grounded measuring junction thermocouple
assembly.
7.5.1.1 The minimum acceptable insulation resistance be-
tween the thermoelements and the sheath while the test
specimen is at the specified elevated temperature shall be as
stated in the standard specification relevant to the subject
thermocouple assembly.
7.5.2 Bulk Cable—Insulation resistance tests on sheathed
(a) Style G Grounded Thermocouple Junction thermocouple cable at elevated temperatures have the purpose
of determining (1) if excess moisture is in the insulation of the
bulk cable, or (2) if the insulation contains excess impurities
other than moisture, which will affect the insulation resistance
at high temperatures.
7.5.2.1 Elevated Temperature, Moisture and Impurities
Combined—The steps listed for this test are intended to
evaluate the combined effects of insulation impurities and
moisture contamination using elevated temperature insulation
(b) Style U Ungrounded Thermocouple Junction
resistance testing of Type K or N bulk cable. Warning—
FIG. 3 Sheathed Thermocouple Assembly
Improper technique in constructing thermocouple assemblies
can introduce additional insulation impurities and moisture
contamination.
and a 2.5 mm (0.1-in.) reticle graduated in at least 0.03 mm
(1) Cut a specimen of approximately 1.2 m (4 ft) in length
(0.001-in.) increments. This measurement test can be done at
from the end of the bulk cable. Strip both ends of the sample
the same time as the measurements in 8.2.4.1 and 9.4.2.
about 25 mm (1 in.) to expose the thermoelements and at once
7.3.2 A radiograph, or a projected enlargement of the
seal the ends with an insulating sealant such as epoxy to
radiograph, can be used with the microscope described in 7.3.1
prevent further moisture absorption. Wind the center section of
to measure the insulation thickness C of Fig. 3 around the
the specimen around a 25 mm (1-in.) mandrel to form three
measuring junction. See also 10.7, Radiographic Inspection.
coils, as shown in Fig. 4. The coils use about 0.3 m (1 ft) of the
7.3.3 Sampling frequency, measurement tolerance, and in-
sulation thickness shall be as stated in the standard specifica-
tion relevant to the subject thermocouple. Examples of speci-
fications for the insulation thickness are given in the Measuring
Junction Configuration section of Specifications E608/E608M
and E2181/E2181M for the junction area, in the General
Dimensional Requirements of Specifications E585/E585M and
E2181/E2181M and in Tables X1.1 and X1.2.
7.4 Insulation Resistance, Room Temperature—Measure the
insulation resistance of sheathed thermocouple cable at room
temperature using Test Method E780. Sampling frequency and
insulation resistance shall be as stated in the relevant invoking
thermocouple specification, or as agreed upon between the
purchaser and the producer. See Table X1.3.
7.5 Insulation Resistance, Elevated Temperatures—The pur-
pose of this test is to determine if the thermocouple insulation
will be adequate for high temperature use of the thermocouple
NOTE 1—The ends of the test specimen are sealed with epoxy to prevent
(Warning—All thermocouples may have changes in thermo-
water vapor from being adsorbed or desorbed during the test.
electric homogeneity produced by exposure to elevated tem-
FIG. 4 High Temperature Insulation Resistance Test Assembly to
peratures; therefore, this test should be regarded as usually Test for Moisture Plus Impurities
E839 − 23
specimen. (1832 °F 6 18 °F). Allow the sample to stabilize at the test
(2) Install a suitable connector on one end of the coil and temperature as measured by the furnace monitor thermocouple
test the room temperature insulation resistance as described in for at least 15 min.
7.4. (6) Measure the insulation resistance at the voltage appro-
(3) Insert the sample coil into a furnace and bring the coil priate for the thermocouple sheath diameter. The charge time of
temperature to 1000 °C 6 10 °C (1832 °F 6 18 °F). The sealed the megohm tester should be at least 1 min before the
ends of the sample should be kept near room temperature. measurement is recorded.
Allow the sample to stabilize at 1000 °C (1832 °F) as mea- (7) Record the resistance between each thermoelement,
sured by the furnace monitor thermocouple for at least 15 min. and from each thermoelement to the sheath.
(4) Measure the insulation resistance at the voltage and
range appropriate for readability and the thermocouple sheath
8. Sheath Properties
diameter. The charge time of the megohm tester should be at
8.1 Sheath Integrity—Leakage of air or moisture into the
least 1 min before the measurement is recorded.
sheath can be detrimental to the life and local homogeneity of
(5) Record the insulation resistance between each
the sheathed thermoelements. Penetrations of the sheath may
thermoelement, and from each thermoelement to the sheath.
be caused by holes left during the fabrication of the sheath
7.5.2.2 Elevated Temperature, Contaminants Other than
tubing, cracks due to welding, holes because of incomplete
Moisture—The steps listed for this test evaluate the effects of
closures at either of the measurement ends, or other mechanical
impurities other than moisture in the insulation using insulation
damage. Two major methods, water penetration and mass
resistance testing of the bulk cable at elevated temperatures.
spectrometer measurements of helium penetration, are com-
(1) Cut a specimen about 0.6 m (2 ft) long from the end of
monly used to assess sheath integrity. The mass spectrometer
the bulk cable to be tested. Strip both ends about 25 mm (1 in.)
method is the most sensitive and the only one that can be used
to expose the thermoelements.
with Style G grounded measuring junction thermocouples.
(2) Weld extension wires to each of the thermoelements
These sheath integrity test methods are given in order of
and to the sheath, as shown in Fig. 5. The extension wires need
increasing test sensitivity and difficulty. Before any sheath
not be the same composition as the thermoelements, but the
integrity tests are performed, wipe the sheath with a rag
extension wire must withstand the temperature of the test and
dampened in solvent, such as alcohol, to remove oily surface
the same composition extension wire should be used for all
contaminants.
connections to the specimen.
8.1.1 Fast Sheath Integrity Test Using Water—This test is
(3) Wind the center section of the specimen around a
usually performed on bulk cable using a less sensitive ohm-
25 mm (1-in.) mandrel to form three coils, as shown in Fig. 5.
meter and a lower voltage test than the test used in 8.1.2; it is
The coils use about 0.3 m (1 ft) of the sample.
the fastest test, intended to detect the larger sheath penetra-
(4) Install a suitable terminal strip or connector to the
tions.
extension wires, as shown in Fig. 5 and test the room
8.1.1.1 Strip one end of the length of sheathed cable to
temperature insulation resistance as described in 7.4.
expose at least 6 mm (0.25 in.) of thermoelements.
(5) Insert the sample coil into a furnace so that the
8.1.1.2 Check the opposite end of the length for any
extension wires are in the same uniform temperature zone as
evidence of shorting of thermoelements to the sheath.
the coil and bring the coil temperature to 1000 °C 6 10 °C
8.1.1.3 Seal the exposed ends of the compacted oxide
insulation with an insulating sealant to prevent the absorption
of water vapor.
8.1.1.4 Using a direct-current (dc) ohmmeter, reading to at
least 20 megohm, connect the ground lead to the cable sheath
and the other test lead to either thermoelement.
8.1.1.5 Then, slowly wipe the length of the sheath with a rag
saturated with cold tap water. Apply a light pressure to the rag
circumferentially around the sheath when wiping and start
wiping from the end opposite the instrument connection.
8.1.1.6 As an alternative, immerse the entire cable length, in
a coil if necessary, in tap water, except for 2 %, but not to
exceed 0.3 m (1 ft), at each end.
8.1.1.7 With the ohmmeter range selection switch on the
most sensitive readable range, interpret any noticeable reduc-
tion of insulation resistance as evidence of a leak in the sheath.
8.1.1.8 The leaking section may be cut from the length of
cable and this test repeated to determine the acceptability of the
remaining portion of the finished length.
NOTE 1—The ends of the test specimen are not sealed, allowing water
8.1.2 Basic Sheath Integrity Test Using Water.
vapor to escape before measuring the insulation resistance
8.1.2.1 Strip one end of the length of sheathed cable to
FIG. 5 High Temperature Insulation Resistance Test, Insulation
Contamination Other Than Moisture expose at least 6 mm (0.25 in.) of thermoelements.
E839 − 23
8.1.2.2 Check the opposite end of the length for any day. If the second sensitivity test shows system sensitivity less
evidence of shorting of thermoelements to the sheath. than the minimum value specified below, repeat all intervening
leak tests on the item being tested.
8.1.2.3 Seal the exposed ends of the compacted oxide
8.1.3.3 Introduce the standard or calibrated leak into the
insulation with an insulating sealant to prevent the absorption
system at the point farthest from the leak detector. The mass
of water vapor.
spectrometer-type helium-leak detector shall demonstrate a
8.1.2.4 Using a megohmmeter on the most sensitive read-
-9
minimum system sensitivity of 3 × 10 standard cubic centi-
able range with an applied voltage at a minimum of 10 Vdc and
meters of helium per second as indicated on the smallest scale
at a maximum of 50 Vdc, measure the insulation resistance
-9
division on the leak detector meter. A leak rate of 6 × 10
between the sheath and thermoelements.
standard cubic centimetres of helium per second shall produce
8.1.2.5 Then, using a clean rag saturated with unheated tap
an additional deflection on the leak-detector meter at least
water dripping from the rag, wipe along the length of the
equal to the deflection produced by the combined background
sheath from the end opposite the instrument connection at a
and noise signal from the leak detector itself. Perform the
rate between 40 mm ⁄s to 50 mm ⁄s (7.9 ft ⁄min to 9.8 ft ⁄min)
system sensitivity test as follows:
applying a light pressure to the rag circumferentially around
(1) With the standard, or calibrated leak at the location
the sheath, thereby forcing the water into and through any
described above, introduce the standard leak into the system.
fissure in the sheath wall. Set the cable aside for at least 30 min
(2) Determine the time required for the leak detector to
after application of the water.
indicate a constant-leak rate caused by the standard leak. The
8.1.2.6 A more discriminating method to ensure detecting
system time response is defined as the time required to obtain
exceptionally small leaks is to immerse the entire length
the constant leak-detector indication.
(coiled if necessary), including the welded measuring junction
(3) Note the constant-leak rate, and use this value to
end, in unheated tap water. Allow up to 2 %, but no more than
determine the system sensitivity.
0.3 m (1 ft) of length on ends with insulating sealant to remain
out of the water. Leave the cable immersed in the water for a 8.2 Sheath Dimensions—The sheath dimension measure-
minimum of 16 h. ments shall apply to either bulk cable or completed thermo-
8.1.2.7 After the exposure to the water as required in 8.1.2.5 couple assemblies.
8.2.1 Sheath Length—Measure the thermocouple assembly
or 8.1.2.6, repeat the insulation resistance test of 8.1.2.4.
Interpret a noticeable reduction in insulation resistance imme- sheath length while the thermocouple assembly is lying straight
on a level surface. Gentle axial tension may be applied to the
diately upon exposure to the water, or after completion of
either technique selected, as evidence of a leak in the sheath. thermocouple assembly to straighten sheath curvature during
measurement. Make the measurements from the tip of the
8.1.2.8 A technique to locate the leak, if one is detected, is
sheath closure to the start of the connector, the moisture seal,
to leave the voltage applied while the sheathed cable is exposed
the transition piece, or the exposed wires (as shown in Fig. 6)
to the water. This will often pinpoint the location of a leak by
using a steel tape or ruler with gradations of 2 mm (0.08 in.) or
emitting bubbles due to the electrolysis of the water.
less.
8.1.2.9 The leaking section of the length of cable may be
8.2.2 Sheath Diameter—Measure the outside diameter of
removed and this test repeated to determine acceptability of the
the sheath at five random points along its length with an optical
remaining portion of the finished length.
comparator, diameter gage, micrometer, or vernier calipers. If
8.1.3 Sheath Integrity, Mass Spectrometer Method:
a micrometre or vernier calipers is used, readings shall be taken
8.1.3.1 Test the sheath and measuring end closure as fol-
lows: Weld, or otherwise hermetically seal the reference
junction end to prevent the detrimental absorption of moisture.
Wipe the test item clean with a cloth saturated with a solvent
such as alcohol. Externally pressurize the sheath and measur-
ing end closure with helium to at least 7.0 Mpa (66 atm) for a
period of 5 to 10 min. Exclude the reference junction end
moisture seal from helium pressurization to preclude damage.
Wipe the test item again with a solvent-saturated cloth and
insert it into a test chamber within 2 h of pressurization.
Evacuate the interior of this chamber to a pressure of 7 kPa
(50 mm Hg) or less, and test for the presence of helium using
a mass spectrometer-type helium-leak detector. Monitor the
test chamber for a time period of at least three times the system
time response (see 8.1.3.3). Take an indication of helium
-6
leakage of 6 × 10 standard cubic centimeters per second as
evidence of a leak.
8.1.3.2 Determine the sensitivity of the leak detector com-
bined with the evacuated test chamber, hereafter called the
system, using a standard leak or a calibrated leak of known
leak rate before and after each test, or group of tests, on a given FIG. 6 Length Measurements of Thermocouple Assemblies
E839 − 23
120° apart at each measurement point. Limits of sheath 8.3.4.1 Cut a test sample about 0.5 m (20 in.) long from one
diameter variation shall be as stated in the standard specifica- end of a bulk cable length and place the specimen in the tension
testing machine as described in 7.2 and shown in Fig. 2.
tion relevant to the subject thermocouple. See Table X1.4.
8.3.4.2 After the tension specimen has been stretched to
8.2.3 Sheath Roundness—The difference between the maxi-
breaking, scrape a fingernail along the sheath surface of the
mum and minimum outside diameter measurements at any of
stretched section; any sharp projections indicate cold-laps in
the points from 8.2.2 shall be considered the roundness. The
the sheath surface.
value of roundness tolerance shall be as stated in the standard
specification relevant to the subject thermocouple. See X1.4.
8.4 Metallurgical Structure of the Sheath—Select samples
8.2.4 Sheath Wall Thickness—Determine the sheath wall of each production run with the location and number of
thickness, dimension B of Fig. 3, using either of the following samples as stated in the specification relevant to the subject
two methods: thermocouple.
8.4.1 Grain Size—Examine a section from the sample ther-
8.2.4.1 A metallographic mount, prepared in accordance
mocouple cable for grain size of the sheath using Practice E3
with Practice E3, of a polished cross section of the thermo-
to prepare the metallographic specimen. Use Test Methods
couple or cable using a microscope having at least a 60×
E112 to determine average grain size.
magnification and a 2.5 mm (0.1-in.) reticle graduated in at
8.4.2 Sheath Wall Defects—Examine the metallographic
least 0.03 mm (0.001-in.) increments. This measurement test
specimen for sheath wall cracks or localized wall thinning,
can be done at the same time as the measurements in 7.3 and
using the method in 8.2.4.
9.4.2.
8.4.3 Acceptance Criteria—The acceptable grain size and
8.2.4.2 A radiograph, or a projected enlargement of the
wall defects acceptance levels shall be agreed upon between
radiograph, can be used with the microscope described in
the purchaser and the producer. Sections 5.1.1 and 6.7 of
8.2.4.1 to measure the sheath wall thickness B of Fig. 3 around
Specification E235 may be used as a guide.
the measuring junction. See also 10.7, Radiographic Inspec-
tion.
8.5 Sheath Ductility:
8.5.1 These tests are useful when it is important for ther-
8.2.4.3 Sampling frequency, sheath wall thickness and al-
lowable variations of the sheath wall thickness shall be as mocouple cable with a sheath of either austenitic stainless steel
or nickel-chromium-iron alloy to be ductile. These are destruc-
stated in the standard specification relevant to the subject
tive tests, performed on one sample from each production run,
thermocouple. Examples of specifications for the sheath wall
unless otherwise specified.
thickness are given in the Measuring Junction Configuration
section of Specifications E608/E608M and E2181/E2181M for 8.5.2 Sharp Bend Test—Closely wind the selected section of
the sheathed thermocouple cable three full turns around a
the junction area, in the General Dimensional Requirements of
Specifications E585/E585M and E2181/E2181M and in Tables mandrel with a diameter twice the sheath diameter. Check the
continuity of each thermoelement and insulation resistance
X1.1 and Table X1.4.
between each thermoelement and the sheath and all other
8.3 Sheath Surface—There are no quantitative tests defining
thermoelements within the cable before and after bending (see
the conditions of the sheath cleanliness or reflectivity, and only
X1.4.1).
semi-quantitative tests for surface roughness. The number of
8.5.2.1 Cut the center turn from the section and examine
pieces of finished thermocouple cable to be tested and the
under 30× magnification. Any visual evidence of sheath
criteria for acceptance shall be as stated in the standard
cracking shall be an indication of failure.
specification relevant to the subject thermocouple.
8.5.3 Tension Test—This test is an alternative to the sharp
8.3.1 Gross Visual—Visually examine the sheath surface of
bend test in 8.5.2 and can be performed at the same time as the
the thermocouple to verify that the sheath appears to be clean
insulation compaction assurance test in 7.2.
and has the specified color and brightness.
8.5.3.1 Cut a test sample about 0.5 m (20 in.) long from one
8.3.2 Surface Finish—Compare the surface of the sheath
end of a bulk cable length and place the sample in the tension
roughness standards in accordance with ANSI B46.1 to ensure
testing machine as described in 7.2 and shown in Fig. 2.
a surface roughness that is no more than specified.
8.5.3.2 Measure the distance between the grips of the
8.3.3 Dye Penetrant Method—Examine the surface of the tension testing machine to establish the initial length, L , of the
sheath for any indications of cracks, seams, holes, or other
test sample that will be elongated.
defects when tested with dye penetrant in accordance with Test
8.5.3.3 Stretch the test sample while recording the applied
Method E165, Procedure A-2. Procedure A-2 is a post-
force and the amount of elongation until the test sample breaks.
emulsifiable fluorescent liquid penetrant inspection method.
8.5.3.4 Find the yield force of the test sample by drawing a
Warning—The Special Requirements section of Test Method
line parallel to the initial straight line but offset by 0.3 % on a
E165 restricts the use of some solvents with some sheath
plot of the force versus elongation (stress-strain plot). The
materials.
yield force is that indicated where the parallel offset line
8.3.4 Sheath Condition Test—This test is intended to detect intercepts the plot (see Fig. 7).
cold-laps in the thermocouple sheath and can be performed at 8.5.3.5 The acceptance criteria for yield force and sheath
the same time as the tension test in 8.5.3 or the insulation rupture shall be as stated in the standard specification relevant
compaction assurance test in 7.2. to the subject thermocouple (see X1.4).
E839 − 23
thermoelements, such as Type E or K, will have changes of
thermoelectric homogeneity produced by this test and the test
should be considered potentially destructive.
9.3.1 Sheathed Thermocouple Drift—Place the thermo-
couple in a protective tube with an inert atmosphere if the
sheath is known to lose its protective ability after contact with
air at the test temperature.
9.3.1.1 Place the test thermocouple in the test furnace so
that it is at the same temperature as a reference thermometer
that has been proven to drift less than 1 % of the acceptance
criteria during the test period.
9.3.1.2 Heat the furnace to the test temperature as stated in
the standard specification relevant to the subject thermocouple
but limited to the upper temperature limits appropriate for the
thermocouple’s sheath material and diameter.
9.3.1.3 After the test thermocouple has stabilized at
temperature, compare the emf of the test thermocouple to the
stable reference thermometer for a period of 2 h.
9.3.1.4 The acceptance criteria for drift stability shall be as
FIG. 7 Tension Test Evaluation of Thermocouples
stated in the standard specification relevant to the subject
thermocouple. A common criterion is that the emf of the
9. Thermoelement Properties
thermocouple assembly should not drift more than the standard
or special tolerances for that type thermocouple (see Table
9.1 Calibration—Test Method E220 describes suitable cali-
X1.6).
bration techniques. Specification E230 lists the temperature-
electromotive force (emf) tables for standard base metal, noble
9.4 Thermoelement Diameter—The thermoelement diam-
metal and refractory metal thermocouples and Guide E1751
eter in the thermocouple assembly can be measured using any
lists temperature-emf tables for selected non-standard thermo-
of the following three methods.
couples. If agreed between the producer and user, Test Method
9.4.1 Strip the sheath and insulation from four random
E207 may be used to calibrate the individual thermoelements
locations to obtain four 25 mm (1 in.) lengths of the thermo-
against a secondary reference standard. Because of varied
elements. Measure the diameter of the thermoelement midway
requirements, calibration temperatures and accuracies shall be
of the sample length with an optical comparator, diameter
specified in the purchase documents. Warning—Type E and K
gage, micrometer, or vernier caliper. If a micrometer or vernier
thermoelements will experience changes in thermoelectric
caliper is used, the readings are to be 120° apart.
homogeneity produced by exposure to temperatures in the
9.4.2 A metallographi
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
´1
Designation: E839 − 11 (Reapproved 2016) E839 − 23 An American National Standard
Standard Test Methods for
Sheathed Thermocouples and Sheathed Thermocouple
Cable
This standard is issued under the fixed designation E839; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Added references to Tables X1.7 and X1.8 to 10.7.4 editorially in December 2016.
1. Scope
1.1 This document lists methods for testing Mineral-Insulated, Metal-Sheathed (MIMS) thermocouple assemblies and thermo-
couple cable, but does not require that any of these tests be performed nor does it state criteria for acceptance. The acceptance
criteria are given in other ASTM standard specifications that impose this testing for those thermocouples and cable. Examples from
ASTM thermocouple specifications for acceptance criteria are given for many of the tests. These tabulated values are not
necessarily those that would be required to meet these tests, but are included as examples only.
1.2 These tests are intended to support quality control and to evaluate the suitability of sheathed thermocouple cable or assemblies
for specific applications. Some alternative test methods to obtain the same information are given, since in a given situation, an
alternative test method may be more practical. Service conditions are widely variable, so it is unlikely that all the tests described
will be appropriate for a given thermocouple application. A brief statement is made following each test description to indicate when
it might be used.
1.3 The tests described herein include test methods to measure the following properties of sheathed thermocouple material and
assemblies.
1.3.1 Insulation Properties:
1.3.1.1 Compaction—direct method, absorption method, and tension method.
1.3.1.2 Thickness.
1.3.1.3 Resistance—at room temperature and at elevated temperature.
1.3.2 Sheath Properties:
1.3.2.1 Integrity—two water test methods and mass spectrometer.
1.3.2.2 Dimensions—length, diameter, and roundness.
1.3.2.3 Wall thickness.
These test methods are under the jurisdiction of ASTM Committee E20 on Temperature Measurement and is the direct responsibility of Subcommittee E20.14 on
Thermocouples - Testing.
Current edition approved Nov. 1, 2011Nov. 1, 2023. Published January 2016November 2023. Originally approved in 1989. Last previous edition approved in 20112016
ɛ1
as E839 – 11.E839 – 11 (2016) . DOI: 10.1520/E0839-11R16E01.10.1520/E0839-23.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E839 − 23
1.3.2.4 Surface—gross visual, finish, defect detection by dye penetrant, and cold-lap detection by tension test.
1.3.2.5 Metallurgical structure.
1.3.2.6 Ductility—bend test and tension test.
1.3.3 Thermoelement Properties:
1.3.3.1 Calibration.
1.3.3.2 Homogeneity.
1.3.3.3 Drift.
1.3.3.4 Thermoelement diameter, roundness, and surface appearance.
1.3.3.5 Thermoelement spacing.
1.3.3.6 Thermoelement ductility.
1.3.3.7 Metallurgical structure.
1.3.4 Thermocouple Assembly Properties:
1.3.4.1 Dimensions—length, diameter, and roundness.
1.3.4.2 Surface—gross visual, finish, reference junction end moisture seal, and defect detection by dye penetrant.
1.3.4.3 Electrical—continuity, loop resistance, and connector polarity.
1.3.4.4 Radiographic inspection.
1.3.4.5 Thermoelement diameter.
1.3.4.6 Thermal response time.
1.3.4.7 Thermal cycle.
1.4 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each
system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the
two systems may result in non-conformance with the standard.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and healthsafety, health, and environmental practices and determine
the applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
E3 Guide for Preparation of Metallographic Specimens
E94 Guide for Radiographic Examination Using Industrial Radiographic Film
E112 Test Methods for Determining Average Grain Size
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
E839 − 23
E165 Practice for Liquid Penetrant Testing for General Industry
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E207 Test Method for Thermal EMF Test of Single Thermoelement Materials by Comparison With Reference Thermoelement
of Similar EMF-Temperature Properties
E220 Test Method for Calibration of Thermocouples By Comparison Techniques
E230 Specification for Temperature-Electromotive Force (emf) Tables for Standardized Thermocouples
E235 Specification for Type K and Type N Mineral-Insulated, Metal-Sheathed Thermocouples for Nuclear or for Other
High-Reliability Applications
E344 Terminology Relating to Thermometry and Hydrometry
E585/E585M Specification for Compacted Mineral-Insulated, Metal-Sheathed, Base Metal Thermocouple Cable
E608/E608M Specification for Mineral-Insulated, Metal-Sheathed Base Metal Thermocouples
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
E780 Test Method for Measuring the Insulation Resistance of Mineral-Insulated, Metal-Sheathed Thermocouples and
Mineral-Insulated, Metal-Sheathed Cable at Room Temperature
E1025 Practice for Design, Manufacture, and Material Grouping Classification of Hole-Type Image Quality Indicators (IQI)
Used for Radiography
E1129/E1129M Specification for Thermocouple Connectors
E1350 Guide for Testing Sheathed Thermocouples, Thermocouple Assemblies, and Connecting Wires Prior to, and After
Installation or Service
E1684 Specification for Miniature Thermocouple Connectors
E1751 Guide for Temperature Electromotive Force (emf) Tables for Non-Letter Designated Thermocouple Combinations
E2181/E2181M Specification for Compacted Mineral-Insulated, Metal-Sheathed, Noble Metal Thermocouples and Thermo-
couple Cable
2.2 ANSI Standard
B 46.1 Surface Texture
2.3 Other Standard
USAEC Division of Reactor Development and Technology RDT Standard C 2-1T Determination of Insulation Compaction in
Ceramic Insulated Conductors August 1970
3. Terminology
3.1 Definitions—The definitions given in Terminology E344 shall apply to these test methods.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 bulk cable, n—a single length of thermocouple cable produced from the same raw material lots after completion of
fabrication.
3.2.2 cable lot, n—a quantity of finished mineral–insulated, metal-sheathed thermocouple cable manufactured from tubing or other
sheath material from the same heat, wire from the same spool and heat, and insulation from the same batch, then assembled and
processed together under controlled production conditions to the required final outside diameter.
3.2.3 cold-lap, n—sheath surface defect where the sheath surface has been galled and torn by a drawing die and the torn surface
smoothed by a subsequent diameter reduction.
3.2.4 insulation compaction density, n—the density of a compacted powder is the combined density of the powder particles and
the voids remaining after the powder compaction. Sometimes the insulation compaction density is divided by the theoretical
density of the powder particles to obtain a dimensionless fraction of theoretical density as a convenient method to express the
relative compaction.
3.2.5 raw material, n—tubing or other sheath material, insulation and wires used in the fabrication of sheathed thermocouple
cable.
3.2.6 short range ordering, n—the reversible short-ranged, order-disorder transformation in which the nickel and chromium atoms
occupy specific (ordered) localized sites in the Type EP or Type KP thermoelement alloy crystal structure.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036.
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3.2.7 thermal response time, n—the time required for a sheathed thermocouple signal to attain the specified percent of the total
voltage change produced by a step change of temperature at the sheath’s outer surface.
4. Summary of Test Methods
4.1 Insulation Properties:
4.1.1 Compaction—These tests ensure that the insulation is compacted sufficiently ((1)1) to prevent the insulation from shifting
during use with the possibility of the thermoelements shorting to each other or to the sheath, and ((2)2) to have good heat transfer
between the sheath and the thermoelements.
4.1.2 Insulation Resistance—The insulation shall be free of moisture and contaminants that would compromise the voltage-
temperature relationship or shorten the useful life of the sheathed thermocouple. Measurement of insulation resistance is a useful
way to detect the presence of unacceptable levels of impurities in the insulation.
4.2 Sheath Properties:
4.2.1 Integrity—These tests ensure that ((1)1) the sheath will be impervious to moisture and gases so the insulation and
thermoelements will be protected, ((2)2) surface flaws and cracks that might develop into sheath leaks are detected, and ((3)3) the
sheath walls are as thick as specified.
4.2.2 Dimensions—Determination of length, diameter, and sheath roundness are often necessary to assure proper dimensional fit.
4.2.3 Sheath Ductility—The sheath shall be ductile enough to bend the required amount without breaking or cracking.
4.3 Thermoelement Properties Service Life:
4.3.1 Calibration—This test ensures that the temperature-emf relationship initially corresponds to standardized tolerances.
4.3.2 Size—The thermocouple sheath and thermoelement sizes are related to the service life and the thermoelement spacing is
related to possible low insulation resistance or shorting.
4.3.3 Thermoelement Ductility—Ductility of the thermoelements shall be sufficient to allow the assembly to be bent during
assembly or service without significant damage to the thermoelements.
4.4 Thermocouple Assembly Properties—The criteria listed above shall apply to both thermocouple assemblies and to bulk cable.
In addition, the following tests are important for thermocouple assemblies.
4.4.1 Continuity—The loop continuity test assures that the thermocouple assembly has a completed circuit.
4.4.2 Loop Resistance—The loop resistance test can detect shorted or damaged thermoelements.
4.4.3 Polarity—The connector polarity test indicates whether the connector is correctly installed.
4.4.4 Moisture Seal—The moisture seal at the reference junction end of the thermocouple, if faulty, may allow contamination of
the insulation with moisture or gases.
4.4.5 Radiography—Radiographic examination of the junction and sheath closure weld can indicate faulty junctions and sheath
closures that will lead to early failure. Most internal dimensions can also be measured from the radiograph.
4.4.6 Response Time—The thermal response time gives an indication of the quickness with which an installed thermocouple will
signal a changing temperature under the test conditions.
4.4.7 Thermal Cycle—The thermal cycle test will offer assurance that the thermocouple will not have early failure because of
strains imposed from temperature transients.
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5. Significance and Use
5.1 This standard provides a description of test methods used in other ASTM specifications to establish certain acceptable limits
for characteristics of methods for characterizing thermocouple assemblies and thermocouple cable. These test methods define how
those characteristics shall be determined.
5.2 The usefulness and purpose of the included tests are given for the category of tests.
5.3 Warning—Users should be aware that certain characteristics of thermocouples might change with time and use. If a
thermocouple’s designed shipping, storage, installation, or operating temperature has been exceeded, that thermocouple’s moisture
seal may have been compromised and may no longer adequately prevent the deleterious intrusion of water vapor. Consequently,
the thermocouple’s condition established by test at the time of manufacture may not apply later. In addition, inhomogeneities can
develop in thermoelements because of exposure to higher temperatures, even in cases where maximum exposure temperatures have
been lower than the suggested upper use temperature limits specified in Table 1 of Specification E608/E608M. For this reason,
calibration of thermocouples destined for delivery to a customer is not recommended. Because the EMFemf indication of any
thermocouple depends upon the condition of the thermoelements along their entire length, as well as the temperature profile pattern
in the region of any inhomogeneity, the EMFemf output of a used thermocouple will be unique to its installation. Because
temperature profiles in calibration equipment are unlikely to duplicate those of the installation, removal of a used thermocouple
to a separate apparatus for calibration is not recommended. Instead, in situ calibration by comparison to a similar thermocouple
known to be good is often recommended.
6. General Requirements
6.1 All the inspection operations are to be performed under clean conditions that will not degrade the insulation, sheath, or
thermoelements. This includes the use of suitable gloves when appropriate.
6.2 During all process steps in which insulation is exposed to ambient atmosphere, the air shall be clean, with less than 50 %
relative humidity, and at a temperature between 20 and 26°C (68 and 79°F).20 °C and 26 °C (68 °F and 79 °F).
6.3 All samples which are tested shall be identified by material code, and shall be traceable to a production run.
7. Insulation Properties
7.1 Insulation Compaction Density—The thermal conductivity of the insulation, as well as the ability of the insulation to lock the
thermoelements into place, will be affected by the insulation compaction density.
7.1.1 A direct method for measuring insulation compaction density is applicable if a representative sample can be sectioned so
that the sample ends are perpendicular to the sample length and the sheath, thermoelements, and insulation form a smooth surface
free of burrs. The procedure is as follows:
7.1.1.1 Weigh the sample section,
7.1.1.2 Measure the sheath diameter and length with a micrometer,
7.1.1.3 Separate the insulation from the thermoelement and sheath with the use of an air abrasive tool,
7.1.1.4 Weigh the thermoelements and sheath, and
7.1.1.5 Determine the sheath and thermoelements densities either by experiment or from references.
7.1.1.6 Determine the percentage of the maximum theoretical insulation density ρ as follows:
%ρ5 100 A 2 B / 0.785 C D 2 E/F1G/H J (1)
~ ! $@ ~ !# %
where:
A = total specimen mass, kg or lb,
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B = sheath and wires mass, kg or lb,
C = sheath diameter, m or in.,
D = specimen length, m or in.,
E = sheath mass, kg or lb,
3 3
F = sheath density, kg/m or lb/in. ,
G = wires mass, kg or lb,
3 3
H = wires density (averaged density if applicable), kg/m or lb/in. , and
3 3
J = maximum theoretical density of the insulation, kg/m or lb/in. .
7.1.2 Alternately, a liquid absorption method for determining the insulation compaction density may be utilized for MIMS samples
with outside diameters 1.5 mm (.062 in.) and larger. This method is based upon a procedure detailed in RDT C 2-1T and requires
the following: (1) the sample ends shall be perpendicular to the sample axis and have a smooth, unglazed surface which will readily
absorb liquid and shall be free of burrs, (2) the outer surfaces of the thermoelements and the inner surface of the sheath shall be
smooth and non-absorbent, and (3) the insulation shall readily support capillary absorption through the entire length of the sample.
This procedure is as follows:
7.1.2.1 Determine the density of kerosene for the temperature at which the measurement is being performed if other than 16ºC
(60ºF).16 ºC (60 ºF).
7.1.2.2 Cut a specimen approximately 2.5 mmcm (1 in.) long.
7.1.2.3 Measure and record the inside diameter of the cable’s sheath and the outside diameter of the cable’s thermoelements to
within .025 mm (.001 in.).
7.1.2.4 Weigh the specimen and record its weight.
7.1.2.5 Measure and record the specimen’s length to within .025 mm (.001 in.) using a vernier caliper.
7.1.2.6 Immerse the specimen in kerosene for a minimum of 24 h.
7.1.2.7 Re-weigh the specimen and record its weight.
7.1.2.8 Determine the percentage of the maximum theoretical insulation density ρ as follows:
2 2
%ρ5 100 12 Y 2 X /0.785 S L O 2 PR (2)
@ ~$ % $ %!#
L = specimen length, cm or in.,
O = inside diameter of sheath, cm or in.,
P = number of thermoelements in the cable,
R = outside diameter of thermoelements, cm or in.,
3 3
S = specific gravity of the kerosene absorbed at 16°C (60°F), .81715 g/cm or .02952 lb/in ,
3 3
S = specific gravity of the kerosene absorbed at 16 °C (60 °F), .81715 g/cm or .02952 lb/in ,
X = weight of the specimen before kerosene is absorbed, g or lb, and
Y = weight of the specimen after kerosene is absorbed, g or lb.
7.2 Insulation Compaction, Assurance Test—This is a destructive test on representative samples that determines if the
thermoelements are locked together with the sheath by the compacted insulation, but this test does not measure the compaction
density per se. This test is the complement of the tests of 7.1 and 7.2 that measures the insulation compaction density but does
not establish that the thermoelements are locked to the sheath, since there is no established minimum compaction density where
locking begins. This test can be performed concurrently with the tension test in 8.5.3.
7.2.1 Cut a test specimen about 0.5 m (20 in.) long from one end of a bulk cable length and strip both ends of the specimen to
expose a minimum of 10 mm (0.4 in.) of the thermoelements.
7.2.2 Without sealing the exposed insulation, clean the thermoelements of insulation to provide good electrical contact and twist
the wires together on one end to form a thermocouple loop (see Fig. 1).
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FIG. 1 Specimen of Sheathed Thermocouple Cable Prepared for Tension Testing
7.2.3 Measure the electrical resistance of the thermocouple loop to 60.01 Ω and measure the length of the thermocouple loop to
establish the electrical resistance per unit length.
7.2.4 Place the test sample in the tension testing machine so that ((1)1) the grips clamp only on the sample sheath, ((2)2) the force
will be applied longitudinally on the sheath, and ((3)3) there is at least a 0.25-m0.25 m (10-in.) distance between the grips where
the force will be applied (see Fig. 2).
7.2.5 Attach an ohmmeter capable of measuring 60.01 Ω to the exposed thermoelements and measure the resistance with no
tension force applied; also measure the distance between the tension tester grips to establish the initial length, L , of the test sample
that will be elongated.
7.2.6 Calculate the initial resistance, R , of the test specimen section that will be elongated, using the unit length electrical
resistance obtained in 7.2.3.
7.2.7 Make a simultaneous record of the electrical resistance and the elongation of the sheath while stretching the test sample until
the thermoelements break.
7.2.8 Examine the exposed ends of the thermoelements to see whether they have been drawn into the insulation during the
elongation; any shortening of the exposed ends indicates low compaction of the insulation.
7.2.9 Plot the fractional change of resistance (∆R/R ) versus the fractional change of length (∆L/L ). The slope of the plot reveals
0 0
if the thermoelements were locked to the sheath throughout the plastic deformation of the sheath and, if not, where the
thermoelements began to elongate in a different manner than the sheath. Examples of criteria to evaluate the insulation locking are
given in X1.9
7.3 Insulation Thickness Measurement—Determine the insulation thickness, dimension C of Fig. 3, using either of the following
methods:
7.3.1 A metallographic mount, prepared in accordance with Practice E3, of a polished cross section of the thermocouple or cable
using a microscope having at least a 60× magnification and a 2.5-mm2.5 mm (0.1-in.) reticle graduated in at least
0.03-mm0.03 mm (0.001-in.) increments. This measurement test can be done at the same time as the measurements in 8.2.4.1 and
9.4.2.
FIG. 2 The Thermocouple Positioned in the Tension Tester
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(a) Style G Grounded Thermocouple Junction
(b) Style U Ungrounded Thermocouple Junction
FIG. 3 Sheathed Thermocouple Assembly
7.3.2 A radiograph, or a projected enlargement of the radiograph, can be used with the microscope described in 7.3.1 to measure
the insulation thickness C of Fig. 3 around the measuring junction. See also 10.7, Radiographic Inspection.
7.3.3 Sampling frequency, measurement tolerance, and insulation thickness shall be as stated in the standard specification relevant
to the subject thermocouple. Examples of specifications for the insulation thickness are given in the Measuring Junction
Configuration section of Specifications E608/E608M and E2181/E2181M for the junction area, in the General Dimensional
Requirements of Specifications E585/E585M and E2181/E2181M and in Tables X1.1 and X1.2.
7.4 Insulation Resistance, Room Temperature—Measure the insulation resistance of sheathed thermocouple cable at room
temperature using Test Method E780. Sampling frequency and insulation resistance shall be as stated in the relevant invoking
thermocouple specification, or as agreed upon between the purchaser and the producer. See Table X1.3.
7.5 Insulation Resistance, Elevated Temperatures—The purpose of this test is to determine if the thermocouple insulation will be
adequate for high temperature use of the thermocouple (Warning—All thermocouples may have changes in thermoelectric
homogeneity produced by exposure to elevated temperatures; therefore, this test should be regarded as usually destructive.)
Sampling frequency shall be as stated in the standard specification relevant to the subject thermocouple.
7.5.1 Thermocouple Assembly—Measure the electrical resistance between the thermocouple circuit and the sheath of a finished
thermocouple assembly with a Style U ungrounded measuring junction (see Fig. 3) using the technique of Test Method E780. Insert
the measuring junction of the finished thermocouple into a furnace or constant temperature bath to a depth that will yield maximum
temperature stability (example: 20 sheath diameters). Then, the thermocouple junction can be heated to the test temperature. This
procedure is not applicable to a Style G grounded measuring junction thermocouple assembly.
7.5.1.1 The minimum acceptable insulation resistance between the thermoelements and the sheath while the test specimen is at
the specified elevated temperature shall be as stated in the standard specification relevant to the subject thermocouple assembly.
7.5.2 Bulk Cable—Insulation resistance tests on sheathed thermocouple cable at elevated temperatures have the purpose of
determining ((1)1) if excess moisture is in the insulation of the bulk cable, or ((2)2) if the insulation contains excess impurities
other than moisture, which will affect the insulation resistance at high temperatures.
7.5.2.1 Elevated Temperature, Moisture and Impurities Combined—The steps listed for this test are intended to evaluate the
combined effects of insulation impurities and moisture contamination using elevated temperature insulation resistance testing of
Type K or N bulk cable. Warning—Improper technique in constructing thermocouple assemblies can introduce additional
insulation impurities and moisture contamination.
(1) Cut a specimen of approximately 1.2 m (4 ft) in length from the end of the bulk cable. Strip both ends of the sample about
25 mm (1 in.) to expose the thermoelements and at once seal the ends with an insulating sealant such as epoxy to prevent further
E839 − 23
moisture absorption. Wind the center section of the specimen around a 25-mm25 mm (1-in.) mandrel to form three coils, as shown
in Fig. 4. The coils use about 0.3 m (1 ft) of the specimen.
(2) Install a suitable connector on one end of the coil and test the room temperature insulation resistance as described in 7.4.
(3) Insert the sample coil into a furnace and bring the coil temperature to 1000 6 10°C (1832 6 18°F).1000 °C 6 10 °C
(1832 °F 6 18 °F). The sealed ends of the sample should be kept near room temperature. Allow the sample to stabilize at 1000°C
(1832°F)1000 °C (1832 °F) as measured by the furnace monitor thermocouple for at least 15 min.
(4) Measure the insulation resistance at the voltage and range appropriate for readability and the thermocouple sheath
diameter. The charge time of the megohm tester should be at least 1 min before the measurement is recorded.
(5) Record the insulation resistance between each thermoelement, and from each thermoelement to the sheath.
7.5.2.2 Elevated Temperature, Contaminants Other than Moisture—The steps listed for this test evaluate the effects of impurities
other than moisture in the insulation using insulation resistance testing of the bulk cable at elevated temperatures.
(1) Cut a specimen about 0.6 m (2 ft) long from the end of the bulk cable to be tested. Strip both ends about 25 mm (1 in.)
to expose the thermoelements.
(2) Weld extension wires to each of the thermoelements and to the sheath, as shown in Fig. 5. The extension wires need not
be the same composition as the thermoelements, but the extension wire must withstand the temperature of the test and the same
composition extension wire should be used for all connections to the specimen.
(3) Wind the center section of the specimen around a 25-mm25 mm (1-in.) mandrel to form three coils, as shown in Fig. 5.
The coils use about 0.3 m (1 ft) of the sample.
(4) Install a suitable terminal strip or connector to the extension wires, as shown in Fig. 5 and test the room temperature
insulation resistance as described in 7.4.
(5) Insert the sample coil into a furnace so that the extension wires are in the same uniform temperature zone as the coil and
bring the coil temperature to 1000 6 10°C (1832 6 18°F).1000 °C 6 10 °C (1832 °F 6 18 °F). Allow the sample to stabilize at
the test temperature as measured by the furnace monitor thermocouple for at least 15 min.
(6) Measure the insulation resistance at the voltage appropriate for the thermocouple sheath diameter. The charge time of the
megohm tester should be at least 1 min before the measurement is recorded.
(7) Record the resistance between each thermoelement, and from each thermoelement to the sheath.
8. Sheath Properties
8.1 Sheath Integrity—Leakage of air or moisture into the sheath can be detrimental to the life and local homogeneity of the
sheathed thermoelements. Penetrations of the sheath may be caused by holes left during the fabrication of the sheath tubing, cracks
due to welding, holes because of incomplete closures at either of the measurement ends, or other mechanical damage. Two major
methods, water penetration and mass spectrometer measurements of helium penetration, are commonly used to assess sheath
integrity. The mass spectrometer method is the most sensitive and the only one that can be used with Style G grounded measuring
junction thermocouples. These sheath integrity test methods are given in order of increasing test sensitivity and difficulty. Before
any sheath integrity tests are performed, wipe the sheath with a rag dampened in solvent, such as alcohol, to remove oily surface
contaminants.
8.1.1 Fast Sheath Integrity Test Using Water—This test is usually performed on bulk cable using a less sensitive ohmmeter and
a lower voltage test than the test used in 8.1.2; it is the fastest test, intended to detect the larger sheath penetrations.
NOTE 1—The ends of the test specimen are sealed with epoxy to prevent water vapor from being adsorbed or desorbed during the test.
FIG. 4 High Temperature Insulation Resistance Test Assembly to Test for Moisture Plus Impurities
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NOTE 1—The ends of the test specimen are not sealed, allowing water vapor to escape before measuring the insulation resistance
FIG. 5 High Temperature Insulation Resistance Test, Insulation Contamination Other Than Moisture
8.1.1.1 Strip one end of the length of sheathed cable to expose at least 6 mm (0.25 in.) of thermoelements.
8.1.1.2 Check the opposite end of the length for any evidence of shorting of thermoelements to the sheath.
8.1.1.3 Seal the exposed ends of the compacted oxide insulation with an insulating sealant to prevent the absorption of water
vapor.
8.1.1.4 Using a direct-current (dc) ohmmeter, reading to at least 20 megohm, connect the ground lead to the cable sheath and the
other test lead to either thermoelement.
8.1.1.5 Then, slowly wipe the length of the sheath with a rag saturated with cold tap water. Apply a light pressure to the rag
circumferentially around the sheath when wiping and start wiping from the end opposite the instrument connection.
8.1.1.6 As an alternative, immerse the entire cable length, in a coil if necessary, in tap water, except for 2 %, but not to exceed
0.3 m (1 ft), at each end.
8.1.1.7 With the ohmmeter range selection switch on the most sensitive readable range, interpret any noticeable reduction of
insulation resistance as evidence of a leak in the sheath.
8.1.1.8 The leaking section may be cut from the length of cable and this test repeated to determine the acceptability of the
remaining portion of the finished length.
8.1.2 Basic Sheath Integrity Test Using Water.
8.1.2.1 Strip one end of the length of sheathed cable to expose at least 6 mm (0.25 in.) of thermoelements.
8.1.2.2 Check the opposite end of the length for any evidence of shorting of thermoelements to the sheath.
8.1.2.3 Seal the exposed ends of the compacted oxide insulation with an insulating sealant to prevent the absorption of water
vapor.
8.1.2.4 Using a megohmmeter on the most sensitive readable range with an applied voltage at a minimum of 10 Vdc and at a
maximum of 50 Vdc, measure the insulation resistance between the sheath and thermoelements.
8.1.2.5 Then, using a clean rag saturated with unheated tap water dripping from the rag, wipe along the length of the sheath from
the end opposite the instrument connection at a rate between 4040 mm ⁄s to 5050 mm mm/s⁄s (7.9 ft (7.9 ⁄min to 9.8 ft/min) ft ⁄min)
applying a light pressure to the rag circumferentially around the sheath, thereby forcing the water into and through any fissure in
the sheath wall. Set the cable aside for at least 30 min after application of the water.
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8.1.2.6 A more discriminating method to ensure detecting exceptionally small leaks is to immerse the entire length (coiled if
necessary), including the welded measuring junction end, in unheated tap water. Allow up to 2 %, but no more than 0.3 m (1 ft)
of length on ends with insulating sealant to remain out of the water. Leave the cable immersed in the water for a minimum of 16
h.
8.1.2.7 After the exposure to the water as required in 8.1.2.5 or 8.1.2.6, repeat the insulation resistance test of 8.1.2.4. Interpret
a noticeable reduction in insulation resistance immediately upon exposure to the water, or after completion of either technique
selected, as evidence of a leak in the sheath.
8.1.2.8 A technique to locate the leak, if one is detected, is to leave the voltage applied while the sheathed cable is exposed to the
water. This will often pinpoint the location of a leak by emitting bubbles due to the electrolysis of the water.
8.1.2.9 The leaking section of the length of cable may be removed and this test repeated to determine acceptability of the
remaining portion of the finished length.
8.1.3 Sheath Integrity, Mass Spectrometer Method:
8.1.3.1 Test the sheath and measuring end closure as follows: Weld, or otherwise hermetically seal the reference junction end to
prevent the detrimental absorption of moisture. Wipe the test item clean with a cloth saturated with a solvent such as alcohol.
Externally pressurize the sheath and measuring end closure with helium to at least 7.0 Mpa (66 atm) for a period of 5 to 10 min.
Exclude the reference junction end moisture seal from helium pressurization to preclude damage. Wipe the test item again with
a solvent-saturated cloth and insert it into a test chamber within 2 h of pressurization. Evacuate the interior of this chamber to a
pressure of 7 kPa (50 mm (50 mm Hg) or less, and test for the presence of helium using a mass spectrometer-type helium-leak
detector. Monitor the test chamber for a time period of at least three times the system time response (see 8.1.3.3). Take an indication
-6
of helium leakage of 6 × 10 standard cubic centimeters per second as evidence of a leak.
8.1.3.2 Determine the sensitivity of the leak detector combined with the evacuated test chamber, hereafter called the system, using
a standard leak or a calibrated leak of known leak rate before and after each test, or group of tests, on a given day. If the second
sensitivity test shows system sensitivity less than the minimum value specified below, repeat all intervening leak tests on the item
being tested.
8.1.3.3 Introduce the standard or calibrated leak into the system at the point farthest from the leak detector. The mass
-9
spectrometer-type helium-leak detector shall demonstrate a minimum system sensitivity of 3 × 10 standard cubic centimeters of
-9
helium per second as indicated on the smallest scale division on the leak detector meter. A leak rate of 6 × 10 standard cubic
centimetres of helium per second shall produce an additional deflection on the leak-detector meter at least equal to the deflection
produced by the combined background and noise signal from the leak detector itself. Perform the system sensitivity test as follows:
(1) With the standard, or calibrated leak at the location described above, introduce the standard leak into the system.
(2) Determine the time required for the leak detector to indicate a constant-leak rate caused by the standard leak. The system
time response is defined as the time required to obtain the constant leak-detector indication.
(3) Note the constant-leak rate, and use this value to determine the system sensitivity.
8.2 Sheath Dimensions—The sheath dimension measurements shall apply to either bulk cable or completed thermocouple
assemblies.
8.2.1 Sheath Length—Measure the thermocouple assembly sheath length while the thermocouple assembly is lying straight on a
level surface. Gentle axial tension may be applied to the thermocouple assembly to straighten sheath curvature during
measurement. Make the measurements from the tip of the sheath closure to the start of the connector, the moisture seal, the
transition piece, or the exposed wires (as shown in Fig. 6) using a steel tape or ruler with gradations of 2 mm (0.08 in.) or less.
8.2.2 Sheath Diameter—Measure the outside diameter of the sheath at five random points along its length with an optical
comparator, diameter gage, micrometer, or vernier calipers. If a micrometre or vernier calipers is used, readings shall be taken 120°
apart at each measurement point. Limits of sheath diameter variation shall be as stated in the standard specification relevant to the
subject thermocouple. See Table X1.4.
8.2.3 Sheath Roundness—The difference between the maximum and minimum outside diameter measurements at any of the points
from 8.2.2 shall be considered the roundness. The value of roundness tolerance shall be as stated in the standard specification
relevant to the subject thermocouple. See X1.4.
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FIG. 6 Length Measurements of Thermocouple Assemblies
8.2.4 Sheath Wall Thickness—Determine the sheath wall thickness, dimension B of Fig. 3, using either of the following two
methods:
8.2.4.1 A metallographic mount, prepared in accordance with Practice E3, of a polished cross section of the thermocouple or cable
using a microscope having at least a 60× magnification and a 2.5-mm2.5 mm (0.1-in.) reticle graduated in at least
0.03-mm0.03 mm (0.001-in.) increments. This measurement test can be done at the same time as the measurements in 7.3 and
9.4.2.
8.2.4.2 A radiograph, or a projected enlargement of the radiograph, can be used with the microscope described in 8.2.4.1 to
measure the sheath wall thickness B of Fig. 3 around the measuring junction. See also 10.7, Radiographic Inspection.
8.2.4.3 Sampling frequency, sheath wall thickness and allowable variations of the sheath wall thickness shall be as stated in the
standard specification relevant to the subject thermocouple. Examples of specifications for the sheath wall thickness are given in
the Measuring Junction Configuration section of Specifications E608/E608M and E2181/E2181M for the junction area, in the
General Dimensional Requirements of Specifications E585/E585M and E2181/E2181M and in Tables X1.1 and Table X1.4 X1.4.
8.3 Sheath Surface—There are no quantitative tests defining the conditions of the sheath cleanliness or reflectivity, and only
semi-quantitative tests for surface roughness. The number of pieces of finished thermocouple cable to be tested and the criteria for
acceptance shall be as stated in the standard specification relevant to the subject thermocouple.
8.3.1 Gross Visual—Visually examine the sheath surface of the thermocouple to verify that the sheath appears to be clean and has
the specified color and brightness.
8.3.2 Surface Finish—Compare the surface of the sheath roughness standards in accordance with ANSI B46.1 to ensure a surface
roughness that is no more than specified.
8.3.3 Dye Penetrant Method—Examine the surface of the sheath for any indications of cracks, seams, holes, or other defects when
tested with dye penetrant in accordance with Test Method E165, Procedure A-2. Procedure A-2 is a post-emulsifiable fluorescent
liquid penetrant inspection method. Warning—The Special Requirements section of Test Method E165 restricts the use of some
solvents with some sheath materials.
8.3.4 Sheath Condition Test—This test is intended to detect cold-laps in the thermocouple sheath and can be performed at the same
time as the tension test in 8.5.3 or the insulation compaction assurance test in 7.2.
8.3.4.1 Cut a test sample about 0.5 m (20 in.) long from one end of a bulk cable length and place the specimen in the tension testing
machine as described in 7.2 and shown in Fig. 2.
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8.3.4.2 After the tension specimen has been stretched to breaking, scrape a fingernail along the sheath surface of the stretched
section; any sharp projections indicate cold-laps in the sheath surface.
8.4 Metallurgical Structure of the Sheath—Select samples of each production run with the location and number of samples as
stated in the specification relevant to the subject thermocouple.
8.4.1 Grain Size—Examine a section from the sample thermocouple cable for grain size of the sheath using Practice E3 to prepare
the metallographic specimen. Use Test Methods E112 to determine average grain size.
8.4.2 Sheath Wall Defects—Examine the metallographic specimen for sheath wall cracks or localized wall thinning, using the
method in 8.2.4.
8.4.3 Acceptance Criteria—The acceptable grain size and wall defects acceptance levels shall be agreed upon between the
purchaser and the producer. Sections 5.1.1 and 6.7 of Specification E235 may be used as a guide.
8.5 Sheath Ductility:
8.5.1 These tests are useful when it is important for thermocouple cable with a sheath of either austenitic stainless steel or
nickel-chromium-iron alloy to be ductile. These are destructive tests, performed on one sample from each production run, unless
otherwise specified.
8.5.2 Sharp Bend Test—Closely wind the selected section of the sheathed thermocouple cable three full turns around a mandrel
with a diameter twice the sheath diameter. Check the continuity of each thermoelement and insulation resistance between each
thermoelement and the sheath and all other thermoelements within the cable before and after bending (see X1.4.1).
8.5.2.1 Cut the center turn from the section and examine under 30× magnification. Any visual evidence of sheath cracking shall
be an indication of failure.
8.5.3 Tension Test—This test is an alternative to the sharp bend test in 8.5.2 and can be performed at the same time as the insulation
compaction assurance test in 7.2.
8.5.3.1 Cut a test sample about 0.5 m (20 in.) long from one end of a bulk cable length and place the sample in the tension testing
machine as described in 7.2 and shown in Fig. 2.
8.5.3.2 Measure the distance between the grips of the tension testing machine to establish the initial length, L , of the test sample
that will be elongated.
8.5.3.3 Stretch the test sample while recording the applied force and the amount of elongation until the test sample breaks.
8.5.3.4 Find the yield force of the test sample by drawing a line parallel to the initial straight line but offset by 0.3 % on a plot
of the force versus elongation (stress-strain plot). The yield force is that indicated where the parallel offset line intercepts the plot
(see Fig. 7).
8.5.3.5 The acceptance criteria for yield force and sheath rupture shall be as stated in the standard specification relevant to the
subject thermocouple (see X1.4).
9. Thermoelement Properties
9.1 Calibration—Test Method E220 describes suitable calibration techniques. Specification E230 lists the temperature-
electromotive force (emf) tables for standard base metal, noble metal and refractory metal thermocouples and Guide E1751 lists
temperature-emf tables for selected non-standard thermocouples. If agreed between the producer and user, Test Method E207 may
be used to calibrate the individual thermoelements against a secondary reference standard. Because of varied requirements,
calibration temperatures and accuracies shall be specified in the purchase documents. Warning—Type E and K thermoelements
will experience changes in thermoelectric homogeneity produced by exposure to temperatures in the 320 to 540°C (600 to
1000°F)320 °C to 540 °C (608 °F to 1004 °F) temperature range. Calibration of Types E and K thermocouple assemblies should
be regarded as a possibly destructive test for subsequent use of the thermocouple assembly and should only be used to characterize
a production run. (See 5.3.)
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FIG. 7 Tension Test Evaluation of Thermocouples
9.1.1 Assembly Calibration Tests:
9.1.1.1 Assemblies selected randomly from the production run shall be calibrated by Test Method E220.
9.1.1.2 The emf of the test assemblies shall be measured at each of the specified temperatures that range to the limits appropriate
for the type and sheath size of thermocouples as shown in Table X1.5 or to lesser limits as stated in the standard specification
relevant to the subject thermocouple.
9.1.1.3 The number of specimens randomly selected from the production run shall be as stated in the standard specification
relevant to the subject thermocouple.
9.2 Homogeneity—Until standardization o
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